During his big immigration speech in Phoenix, Donald Trump reaffirmed that under his administration, Mexico would pay for a security wall along the southern U.S. border.

“We will build a great wall along the southern border! … And Mexico will pay for the wall, 100 percent. They don't know it yet, but they're going to pay for the wall."

The declaration comes after Mexican president Enrique Peña Nieto said that he told Trump that Mexico would not pay for a wall.

"At the start of the conversation with Donald Trump, I made it clear that Mexico will not pay for the wall," Peña Nieto tweeted, after their meeting.

The tweet followed a joint press conference, during which Trump told a reporter that the wall was discussed but the payment of it was not.

"Who pays for the wall? We didn't discuss," he said. "We did discuss the wall. We didn't discuss payment of the wall. That'll be for a later date. This was a very preliminary meeting."